This is a component of a team project involving collaborators at the Smithsonian Institution and Old Dominion University to study vertical mixing and the impact of UV in the Ross Sea. Although progress has been made regarding UV effects on many parameters such as phytoplankton photosynthesis, bacterial production, and DNA damage, little is known about responses in systems dominated by Phaeocystis Antarctica. The Ross Sea is of interest because of the occurrence of open water at a far southerly location in the spring, well within the "ozone hole," and continuous daylight, with implications for the regulation of DNA repair. The proposed research, which involves determinations of spectral and temporal responses of phytoplankton and bacterioplankton to UV, will be the first in-depth study of UV effects in the Ross Sea and will provide a valuable comparison with our previous work in other Antarctic environments including the Weddell-Scotia Confluence and Palmer Station regions. It will also enhance our understanding of vertical mixing processes, trophic interactions and biogeochemical cycling in the Ross Sea.